(S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate

Skin irritation / corrosion

Administrative data

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-10-17 - 2016-11-28 (experimental phase)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2016

Report date:

2016

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method)

Version / remarks:

Organisation for Economic Co-operation and Development (OECD), OECD Guidelines for Testing of Chemicals, Guideline no. 439: In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method (adopted 28 July 2015)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.46 (In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test)

Version / remarks:

European Community (EC). Commission regulation (EC) No. 440/2008, Part B: Methods for the Determination of Toxicity and other health effects, Guideline B.46 “In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test ". Official Journal of the European Union No. L142; Amended by EC No. 640/2012 OJ No. L193, 20 July 2012

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

(S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate

EC Number:

257-581-0

EC Name:

(S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate

Cas Number:

51988-14-8

Molecular formula:

C9H6N2OS3

IUPAC Name:

phenyl[(5-sulfanylidene-4,5-dihydro-1,3,4-thiadiazol-2-yl)sulfanyl]methanone

Test material form:

solid: particulate/powder

Specific details on test material used for the study:

Irritant or corrosive: Yes
pH (1% in water, indicative range) 4.6 – 4.6 (determined by CRO)

In vitro test system

Test system:

human skin model

Source species:

human

Cell type:

non-transformed keratinocytes

Cell source:

other: SkinEthic Laboratories, Lyon, France

Source strain:

other: n/a, human

Details on animal used as source of test system:

n/a

Justification for test system used:

In the interest of sound science and animal welfare, a sequential testing strategy is recommended to minimise the need of in vivo testing. One of the validated in vitro skin irritation tests is the EPISKIN test, which is recommended in international guidelines (e.g. OECD and EC).

Vehicle:

unchanged (no vehicle)

Details on test system:

RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: EPISKIN Small ModelTM (EPISKIN-SMTM, 0.38 cm2)
- Tissue batch number(s): Batch no.: 16-EKIN-047 (16-EKIN-042)
- Production date: TDS dated 2016-11-22 (2016-10-18), expiration date 2016-11-28 (2016-10-24)

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: All incubations, with the exception of the test item incubation of 15 minutes at room temperature, were carried out in a controlled environment, in which optimal conditions were a humid atmosphere of 80 - 100% (actual range 67 - 89%), containing 5.0 ± 0.5% CO2 in air in the dark at 37.0 ± 1.0°C (actual range 35.7 - 38.5°C). Temperature and humidity were continuously monitored throughout the experiment.
- Temperature of post-treatment incubation (if applicable): After incubation, killed epidermis was stored at ≤ -15°C.

REMOVAL OF TEST MATERIAL AND CONTROLS
-Volume and number of washing steps: The skin was moistened with 5 μl Milli-Q water. After the exposure period of 15 ± 0.5 minutes at room temperature, the tissues were washed with phosphate buffered saline to remove residual test item. After rinsing, the cell culture inserts were each dried carefully and moved to a new well on 2 ml pre-warmed maintenance medium until all tissues were dosed and rinsed. After incubation, cell culture inserts were dried carefully to remove excess medium.
- Observable damage in the tissue due to washing: none stated
- Modifications to validated SOP: none stated

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- MTT concentration: 0.3 mg/ml in PBS
- Incubation time: 3h at 37°C
- Spectrophotometer: TECAN Infinite® M200 Pro Plate Reader.
- Wavelength: 570 nm

NUMBER OF REPLICATE TISSUES: 3 tissues per test item

CONTROL TISSUES USED IN CASE OF MTT DIRECT INTERFERENCE
not required, no interference

NUMBER OF INDEPENDENT TEST SEQUENCES / EXPERIMENTS TO DERIVE FINAL PREDICTION: 2

PREDICTION MODEL / DECISION CRITERIA (choose relevant statement)
A test item is considered irritant in the skin irritation test if:
The relative mean tissue viability of three individual tissues after 15 minutes of exposure to the test item and 42 hours of post incubation is ≤ 50% of the mean viability of the negative controls.
A test item is considered non-irritant in the in vitro skin irritation test if:
The relative mean tissue viability of three individual tissues after 15 minutes of exposure to the test item and 42 hours of post incubation is > 50% of the mean viability of the negative controls.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): neat, 11.1 to 16.9 mg
- Concentration (if solution): The skin was moistened with 5 μl Milli-Q water (Millipore Corp., Bedford, Mass., USA) to ensure close contact of the test item to the tissue.

NEGATIVE CONTROL
- Amount(s) applied (volume or weight): 25 μl PBS

POSITIVE CONTROL
- Amount(s) applied (volume or weight): 25 μl 5% SDS, the positive control was re-spread after 7 minutes contact time.

Duration of treatment / exposure:

After the exposure period of 15 ± 0.5 minutes at room temperature, the tissues were washed with phosphate buffered saline to remove residual test item.

Duration of post-treatment incubation (if applicable):

After rinsing, the cell culture inserts were each dried carefully and moved to a new well on 2 ml pre-warmed maintenance medium until all tissues were dosed and rinsed. Subsequently the skin tissues were incubated for 42 hours at 37°C.

Number of replicates:

The test was performed on a total of 3 tissues per test item together with negative and positive controls.
For cell viability measurement, the amount of extracted formazan was determined spectrophotometrically at 570 nm in duplicate
Also, in cell viability measurement, in the initial assay, the untreated death skin had a viability of 82%. Therefore the assay was not considered valid and was repeated.

Results and discussion

In vitro

Results

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

relative mean tissue viability

Value:

97

Vehicle controls validity:

not applicable

Negative controls validity:

not applicable

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Remarks:

Since the mean relative tissue viability for the test item was above 50% the test item is considered to be non-irritant. SD was 1%.

Other effects / acceptance of results:

- OTHER EFFECTS:
- Visible damage on test system: none stated
- Direct-MTT reduction: The non-specific reduction of MTT by the test item was -1.6% of the negative control tissues. Since the %NSMTT ≤ 0.0, there is no need to correct for this interaction.
- Colour interference with MTT: The test item was checked for colour interference in aqueous conditions and for possible direct MTT reduction by adding the test item to MTT medium. Because a colour change was observed by adding MTT-medium it was concluded that (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate did interact with the MTT endpoint.

ACCEPTANCE OF RESULTS:
- Acceptance criteria met for negative control: OD570 values were within historical control data and the Standard Deviation value (SD) of the % viability was <=18.
- Acceptance criteria met for positive control: yes
- Acceptance criteria met for variability between replicate measurements: yes

Applicant's summary and conclusion

Interpretation of results:

GHS criteria not met

Conclusions:

The study was conducted under GLP according to OECD guideline 439 on the registered substance itself. The method is to be considered scientifically reasonable with no deficiencies in documentation or any deviations, the validity criteria are fulfilled, positive and negative controls gave the appropriate response. Hence, the results can be considered as reliable to assess the irritating potential of the test substance to the skin in vitro. The relative mean tissue viability obtained after 15 ± 0.5 minutes treatment with the test item compared to the negative control tissues was 97%. Since the mean relative tissue viability for the test item was above 50% the test item is considered to be non-irritant. It is concluded that this test is valid and that (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate is non-irritant in the in vitro skin irritation test under the experimental conditions described in this report and should not be classified according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) of the United Nations.

Executive summary:

In vitro skin irritation test was performed with (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl)benzenecarbothioate using a human skin model according to OECD 439 under GLP.

This report describes the ability of (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate to induce skin irritation on a human three dimensional epidermal model (EPISKIN Small model (EPISKIN-SM^TM)). The possible skin irritation potential of (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate was tested through topical application for 15 minutes.

The study procedures described in this report were based on the most recent OECD and EC guidelines.

Batch Z900247673 of (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate was an off-white solid. Skin tissue was moistened with 5 µl of Milli-Q water and at least 10 mg of (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate was applied directly on top of the skin tissue for 15士0.5 minutes. After a 42 hour post-incubation period, determination of the cytotoxic (irritancy) effect was performed. Cytotoxicity is expressed as the reduction of mitochondrial dehydrogenase activity measured by formazan production from MTT at the end of the treatment.

The test item did interact with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT). In addition to the normal procedure, three killed tissues treated with test item and three killed untreated tissues were used for the cytotoxicity evaluation with MTT. The non­specific reduction of MTT by the test item was -1.6% of the negative control tissues. Since the %NSMTT < 0.0, there is no need to correct for this interaction.

Skin irritation is expressed as the remaining cell viability after exposure to the test item. The relative mean tissue viability obtained after 15士0.5 minutes treatment with the test item compared to the negative control tissues was 97%. Since the mean relative tissue viability for the test item was above 50% after 15士0.5 minutes treatment the test item is considered to be non-irritant.

The positive control had a mean cell viability of 11% after 15士0.5 minutes exposure. The absolute mean OD570 (optical density at 570 nm) of the negative control tissues was within the laboratory historical control data range. The standard deviation value of the percentage viability of three tissues treated identically was less than 17%, indicating that the test system functioned properly.

Finally, it is concluded that this test is valid and that (S)-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl) benzenecarbothioate is non-irritant in the in vitro skin irritation test under the experimental conditions described in this report.